It's a significantly stronger argument because you don't have to forfeit reason. If your only goal is to remove any ability to justify an attack then you can make up anything you want. For example: "It was aliens driving the boat with secret cloaking technology, and they didn't even come from Venezuela." Is that a stronger argument? Obviously not. The stronger argument is the one that's harder to refute, not the one that's trivial to.

It's not very tenuous really. There's a common design used for this, that isn't used for any other purpose as far as I'm aware. There's no comfort built in, so it's not like a consumer boat. They're built for speed, but also with a lot of cargo space, so they aren't like a fishing boat or anything else. We have many instances of them being boarded and drugs seized from the past, and they look almost identical. The boats also were loaded with some kind of cargo (we can't know what, because it was destroyed, but we know there was stuff in there). Here's a picture:

It's much easier to argue the regime is doing something illegal starting from a place of reason. If they wanted to stop them they easily could have boarded them (though also illegal where they are). Slaughtering the is illegal and immoral, no matter the justification. You can also point out that Venezuela has huge oil reserves, which is a trend for nations we invade. It isn't about drugs. Usually they talk about fentanyl, but that's not coming through Venezuela, so that's a big hole in their reasoning.

There's a lot of ways to approach it that don't require burying your head in the sand and arguing that there aren't drugs being smuggled. Theres far too much evidence for that.